With regard to the thermoplastic polyester elastomer, there have been already known the ones which contain crystalline polyester (such as polybutylene terephthalate (PBT) or polybutylene naphthalate (PBN)) as a hard segment and polyoxyalkylene glycol (such as poly(tetremethylene oxide)glycol (PTMG)) and/or polyester (such as polycaprolactone (PCL) and polybutylene adipate (PBA)) as soft segment(s). They have been practically used already (for example, Patent Documents 1 and 2).
However, it has been known that, although an elastomer of a polyester-polyether type using polyoxyalkylene glycol as a soft segment is excellent in terms of water resistance and low-temperature characteristics, such elastomer is inferior in terms of thermal aging resistance. Also, it has been known that, although an elastomer of a polyester-polyester type using polyester as a soft segment is excellent in terms of thermal aging resistance, such elastomer is inferior in terms of water resistance and low-temperature characteristics. Accordingly, there has been a demand for providing a thermoplastic polyester elastomer which has well-balanced thermal aging resistance and water resistance.
For example, there have been proposed a block polyether-ester copolymer composition wherein polyamide resin, antioxidant of a hindered phenol type, antioxidant of a sulfur type and/or antioxidant of a phosphorus type are/is added to a polyether ester block copolymer (Patent Document 3); and a polyester elastomer resin composition wherein antioxidant of an aromatic amine type, antioxidant of a hindered phenol type, antioxidant of a sulfur type, antioxidant of a phosphorus type and/or polyamide resin are/is added to an elastomer of a polyester type (Patent Document 4). However, in accordance with the constitution as such, there is a problem that thermal aging resistance is still insufficient for car parts or particularly for the use wherein so much thermal aging resistance is required such as for parts around the engine of the car.
There has been also proposed a thermoplastic elastomer resin composition wherein a thermal resisting agent consisting of one or more of antioxidant of an aromatic amine type, antioxidant of a hindered phenol type, antioxidant of a sulfur type and antioxidant of a phosphorus type is/are added to a thermoplastic elastomer prepared by mixing a polyester elastomer consisting of a flexible polyester block copolymer and a highly hard polyester block copolymer with a dynamically cross-linked thermoplastic elastomer (Patent Document 5). Also, there has been proposed a thermoplastic elastomer resin composition wherein glycidyl-modified polyolefin, antioxidant and polyamide resin are added to a thermoplastic elastomer prepared by mixing polyester block copolymer having a hard segment constituted from terephthalic acid and other dicarboxylic acid with polyester resin (Patent Document 6).
However, although improvement in thermal aging resistance is achieved in Patent Document 5 and Patent Document 6, a problem that hydrolysis is apt to happen (which is a problem specific to a polyester resin) has not been solved yet.